A semiconductor light emitting device is a semiconductor device capable of emitting light of various colors due to the recombination of electrons and electron holes at a junction between p-type and n-type semiconductor layers thereof when current is applied thereto. The semiconductor light emitting device has various advantages such as a relatively long lifespan, low power consumption, superior initial driving characteristics and high vibration resistance as compared with a filament-based light emitting device, such that demand therefor has been continuously increasing.
In particular, a group III nitride semiconductor capable of emitting blue light in a single wavelength region has recently come to prominence. In general, since a group III-element nitride such as gallium nitride (GaN), aluminum nitride (AIN) or the like has excellent thermal stability and a direct transition type energy band structure, the group III-element nitride has received considerable attention as a material for a photoelectric device in a wavelength range from blue to ultraviolet. In particular, blue and green light emitting devices using gallium nitride (GaN) have been applied to various devices in various fields of application such as large scale natural colored flat panel displays, traffic lights, indoor lighting devices, high density light sources, high resolution output systems, optical communications systems, and the like.
A group III-element nitride semiconductor layer is grown on a heterogeneous substrate, including: sapphire having a hexagonal structure, silicon carbide (SiC), silicon (Si), or the like; through a process, such as metal organic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), or the like. However, when a group III-element nitride semiconductor layer is grown on a heterogeneous substrate, cracks in the semiconductor layer or warpage thereof may occur and dislocation may be caused due to differences in lattice constants and coefficients of thermal expansion between the semiconductor layer and the substrate. Such cracks in the semiconductor layer, warpage, and dislocation may deteriorate characteristics of a light emitting device. Thus, a buffer layer has been used to alleviate stress due to differences in lattice constants and coefficients of thermal expansion between the semiconductor layer and the substrate.
However, even with the use of the buffer layer, defects of cracks being generated in the semiconductor layer and substrate breakage caused by the differences in lattice constants and coefficients of thermal expansion between the semiconductor layer and the substrate have still occurred.